The present invention relates to a filter device for the filtration of fluids. In particular, one or more embodiments of the present invention relates to filter devices for use in dialysis-type treatments and for filtration processes similar to and related to the hemodialysis process, such as hemofiltration, hemodiafiltration and ultrafiltration, as well as to a method for making a housing of a filtration device.
Filter devices having hollow fibers or membranes are used, for example, in the area of dialysis for a wide variety of purposes. Such filters may be referred to as dialysers, these being used for example in hemodialysis, in which blood is directed into and along the inside of the semi-permeable walls of the hollow fibers while dialysis fluid is directed around the outside of the hollow fibers. Various convection and diffusion processes may thereby take place across the walls of the hollow fibers. These processes serve, for example, to purify and to remove excess fluid from the blood. Additionally, the electrolyte concentration in the blood can be conditioned using infusion fluids, and buffers such as bicarbonate or acetate can be added to the blood. The hemodialysis process is effective at removing substances having a low molecular weight, but may be less effective at removing substances having a middle molecular weight. Low molecular weight substances in the context of dialysis typically includes substances such as urea, having a molecular weight below 5 kDa.
Filter devices of this type may also be employed in so-called hemofiltration, in which a substitution fluid is added to the blood. According to this process, the blood is directed through the inside of the hollow fibers, although in this case no dialysis fluid is passed around the outside of the fibers. Here, excess fluids, in particular water as well as waste products, are removed from the blood by means of a pressure difference across the membrane, here comprised by the semi-permeable walls of the hollow fiber. The substitution fluid can be added either prior or subsequent to the filtration in pre- or post-dilution modes. Hemofiltration is more effective at removing substances having a so-called middle molecular weight lying within the range between approximately 5 kDa- and 0 kDa such as Beta-2-Microglobulin.
A further application for the present type of filter device includes hemodiafiltration: a combination of hemodialysis and hemofiltration, in which dialysate flows across one side of the membrane while blood flows across the other side and at the same time, a pressure gradient exists across the membrane. Infusion fluid may be added to the blood either prior to or after the filtration. This process can results in a higher filtration rate and is especially effective at removing substances having a low and middle molecular weight.
A further process for which such filters are may be used is known as plasmapheresis, in which aqueous blood plasma is filtered out of the blood and returned to the blood after treatment.
Such filter devices are also used in filtration processes such as reverse osmosis wherein undesirable substances may be removed from blood, water or other fluids.
The above-mentioned filter devices can equally be used as so-called ultrafilters for the production of substitution or infusion fluids. In this case, infusion fluid may be directed into the filter across one side of a semi-permeable membrane, and is filtered across the membrane by means of a pressure difference. In this way, the infusion fluid can be sterile-filtered by removal of endotoxins, bacteria and other contaminants. Ultrafilters generally have a similar construction to dialyser-type filters although they are generally smaller in dimension and are not generally used as dialysers in the dialysis process. Ultrafilters are usually employed during a blood filtration treatment in addition to a dialysis filter, the filtrate from the ultrafilter creating the infusion fluid which is then being fed into the blood either on the blood side of the dialysis filter device or into blood in the blood tubes.
These filter devices are usually so constructed that the hollow fibers are arranged as a loose bundle lying longitudinally within a tubular housing. The housing is provided at each end with an end cap and the hollow fiber bundle is arranged between the ends of the housing so that the end cap enclose the ends of the hollow fiber bundle. The ends of the fibers are usually embedded within and secured by a potting compound made from a two-component polymer resin. Except as noted below, the potting compound completely surrounds the ends of the hollow fibers and is molded to the inside of the ends of the housing to create a seal between the header chamber and the inside of the tubular housing.
The extreme ends of the hollow fibers which constitute the hollow fiber bundle open out above the potting compound into a hollow space (hereafter: header chamber) located between the end cap and the end of the hollow fiber bundle. It is therefore possible, with the appropriate arrangement of inlets and outlets, to provide, in a known manner various forms of filter such as the previously mentioned hemodialysis filters, hemofilters, hemodiafilters, ultrafilters etc. Examples of the previously mentioned filters are disclosed in EP-0 305 687, EP-0 355 325 and EP-0 525 317.
The previously mentioned filters or dialysers have certain features in common, namely, that a first fluid may be directed into and through the inside of the semi-permeable hollow fibers. This first fluid may exit from the fiber column having had certain substances removed and possibly certain substances added. A second fluid may be present on the outside of the hollow fibers. This second fluid can either flow through the housing, past and around the hollow fibers, via appropriately located inlet and outlet means, or it can be removed from the first fluid and directed out of the housing via a suitable outlet, for example by means of a pressure differential across the hollow fiber membrane. This second fluid may be a purified form of the first fluid, a dialysis fluid for the exchange of substances into and out of the first fluid across the hollow-fiber membranes, or a waste fluid removed from the first fluid, among others.
If one of the aforementioned filters is applied in the area of dialysis, for example in hemodialysis, various fluid lines (conduits) are connected to it. These fluid lines on the one hand lead blood from the patient to the blood side of the filter and then back to the patient. Additional fluid lines lead the dialysis fluid from a dialysis fluid supply, controlled by a dialysis machine, also sometimes referred to as a dialysis monitoring device, to the dialysate side of the filter and after passage through the filter further to a drain. The blood side here refers to the area of the filter through which the blood of the patient is led, while the dialysate side refers to the area of the filter or the filter housing through which the dialysis fluid is lea. The blood side and the dialysate side are separated from each other in the filter housing by the one or more semi-permeable membrane(s) and these sides correspond respectively to the sides along which the previously mentioned first and second fluids pass.
In order to improve the effectiveness of blood filtration treatments, it is known to use more than one filtration process or filter device connected in series. Thus, as an example, a hemofiltration process may be combined in series with a hemodialysis or hemodiafiltration process, thereby necessitating more than one filter device.
It has further been proposed to combine more than one filtration device within a single housing. A filter cartridge comprising more than one filtration compartment is disclosed for example in WO 02/47785. According to the device disclosed in this document, two hollow fiber bundles are arranged in adjacent compartments which are separated by a wall in which a communicating aperture is provided for the flow of filtrate or dialysate through both compartments.
Additional considerations with regard to the use of such filtration devices are also relevant for their design. When setting up known filter devices prior to a filtration treatment, a number of set-up operations are required to be performed by trained personnel. In particular, extracorporeal blood tubes as well as any necessary dialysis fluid tubes must be connected to the appropriate fluid flow ports of the filter device. In addition, a separate ultrafilter is often desired, usually required to be connected to an infusion fluid supply. This must be carried out with care, as the tubes must be connected correctly in order to avoid potential dangers arising from an incorrect set-up. The set-up stage can be time consuming and therefore reduces the number of treatments which can be carried out using a particular monitoring device. In addition, the requirement to use a separate filter device for ultrafiltration, as well as possibly more than one filter device for filtering blood, increases the equipment costs for each treatment and also the number of connections required.
A further dialyser device is known from DE-A-196 07 162, in which a filtration device for substitution fluid is disclosed along with a hemodiafiltration device integrated within a single housing. Filter membrane means in the form of hollow fibers are provided within both compartments. One end of the hollow fibers of the filter for a substitution fluid is sealed off by means of potting compound or by a cover. A problem encountered with this device is that it is difficult to completely expel all of the air contained within the compartment for the substitution fluid at the start of a filtration process, both the air around the outside of the hollow fibers and in the inside of the fibers. Air on the inside of the fibers is pushed by liquid passing across the membranes into a header chamber at either the blood entry or exit of the dialysis compartment thereby causing unnecessary contact between blood and air in the blood flow circuit. This may be avoided by passing substitution fluid through the filtration compartment prior to passing blood through the hemodiafiltration compartment although this involves additional work for an operator. In addition, air around the outside of the membranes is not completely expelled during the initiation phase of filtration and may be fed through into the blood during a treatment. This increases the thrombogenicity of the blood filtration process. A further drawback of this disclosure exists in that filtration of the substitution fluid takes place from the outside through to the inside of the hollow fiber membranes. This necessitates using a different kind of hollow fiber than those used for the filtration of blood in the hemodiafiltration process in the neighboring chamber, because the direction of the pore size gradient across the membrane thickness requires to be inversed. This requirement greatly complicates the manufacturing requirement of such a device. In addition, when manufacturing a device according to this disclosure, the filling of the respective compartments with hollow fibers is rendered complex and costly.